The present invention relates to methods and apparatus for improving the resistance between a gate conductor and an active area of an antifuse programming elements.
In integrated circuit manufacturing, it is desirable to provide the ability to select various circuit components and/or circuits from an array. For example, redundant parallel circuits may be formed in an integrated circuit and, after testing a given circuit to ensure that it functions properly, the other parallel circuits may be removed. Conversely, a parallel circuit may also be added. While fuses are used to remove unwanted circuit components or circuits, antifuses are employed to add circuits or circuit components. Antifuse elements are normally electrically open, or non-conducting, and are programmable to permit a user to “blow” the element in order to create a useable short circuit.
Various conventional antifuses exist in the art in order to provide the ability to select circuits or circuit components as appropriate. Many of the conventional antifuses require the application of energy by means of external intervention in order to program the antifuse element. Antifuse elements that may be programmed (or blown) by applying an electrical voltage are desirable.
A conventional antifuse element may be formed utilizing a planar transistor structure, such as a MOSFET structure. The conventional antifuse construction includes a semiconductor substrate having an active area, a gate conductor disposed above the semiconductor substrate, and a dielectric insulator disposed between the semiconductor substrate and the gate conductor. When viewed from above, the active area is considerably larger than the gate conductor and the periphery of the gate conductor is contained entirely within the boundaries of the active area. The antifuse is programmed by applying a voltage potential of sufficient magnitude between the gate conductor and the active area of the semiconductor substrate to break down the dielectric.
The electrical resistance between the gate conductor and the active area of the semiconductor substrate of the conventional antifuse structure ranges from about 1 kOhm to about 100 kOhm. Unfortunately, this rather large range of resistance significantly reduces the fuse latch margin and results in an attendant poor performance. Accordingly, there are needs in the art for new methods and apparatus for providing an antifuse function that result in blown antifuse resistances of less than about 1 kOhm and/or that do not vary significantly.